1. Field of the Invention:
The invention is directed to an improved horizontal vacuum belt filter.
2. Description of Related Art:
In the known horizontal belt filters, the filter cloth is generally endless and is first passed over a vacuum belt filter in which a reduced pressure or vacuum, applied through the filter cloth, causes liquid to be sucked out of the filter cake which lies on the filter cloth. The filter cake is thrown off at the end of such a belt filter and the filter cloth is returned to the front end of the belt filter where it receives fresh suspension which is to be dewatered. Often, however, the dewatering action is not adequate so that additional measures must be taken. Thus, there has been utilized a filter system in which a belt filter is followed by a belt press wherein the filter cloth with the filter cake is passed around a drum in a U-shaped loop with pressing rollers pressing the filter cloth and the filter cake against the periphery of the drum and in so doing compacting the filter cake and further dewatering it. In the arrangement just described, the belt filter and the belt press generally have their own separate drives for the circulating filter cloth. Insofar as belt presses of that kind are previously known, the filter cloth is driven in the belt press by a drive roller which lies outside the drum. In that arrangement the drive roller firstly drives an endless pressing belt which by means of direction-changing rollers passes in a U-shaped loop around the drum, wherein the filter cloth with the filter cake is arranged between the pressing belt and the drum. The pressing belt which is driven in that way now entrains the filter cloth lying thereon, by direct frictional engagement. As the pressing belt and the filter cloth are laid around the drum in a U-shaped loop, they already apply a considerable force to the bearings of the drum, which is compensated by a corresponding counteracting force in the bearings of the direction-changing rollers of the pressing belt. The corresponding frictional forces in the bearings of the drum are additionally further increased by pressing rollers which press from the outside against the pressing belt and the filter cloth. When the filter cloth is driven, it transports the filter cake and drives the drum at the periphery of the latter, with the drum in practice rolling against the filter cake. The frictional forces which are to be overcome in the bearings of the drum in that arrangement can produce a considerable tension in the filter cloth. That is especially the case if a shearing action on the filter cake is to be produced by additionally braking the drum, in order in that way to improve the dewatering effect. The filter cloth which ultimately is driven by the friction of the pressing belt is subjected to a relatively high rate of water in that arrangement, it is subjected to stretching and finally it may even tear.